1. Field of the Invention
This invention relates to orthopedic casts and devices for making same.
2. Description of the Prior Art
Numerous attempts have been made to produce a light weight, waterproof and breathable, i.e., air permeable, orthopedic cast which can be readily and easily fabricated by the physician and applied to the patient. The disadvantages of the conventional plaster of paris casts are well known, i.e., such casts are relatively heavy, have little or no resistance to water, i.e., disintegrate when wet, and are not porous to air or water vapor, i.e., have poor breathability. All of this makes them uncomfortable to wear. In particular, the poor breathability causes perspiration to accumulate on the patient's skin with consequential itching and maceration. Additionally, in the preparation of plaster of paris tapes for application as a cast, they must be saturated with water. This penetrates the underwrap which contributes to the maceration of the skin. Finally, such casts have poor X-ray transparency and generate considerable dust upon removal.
In order to avoid these disadvantages, attempts have been made to use two-component resin systems which are applied to fabric tapes and which can be cured either by water, catalysts, or ultraviolet irradiation.
The delivery systems for such two component hardenable materials have presented problems. In the attempt to fashion devices which would maintain the components apart from one another until the actual time of use and then provide a mechanism for mixing of the components and impregnation of the tape, rather complicated mechanisms have been developed. Such a device is disclosed in U.S. Pat. No. 4,131,114. This patent also outlines the other attempts of the prior art to create comparable systems for this purpose.
The hardening or curing of such resins has also produced problems. For example, for those systems which are UV curable, relatively expensive UV irradiation equipment is required making the economics of such UV curable resin systems unfavorable. Also, such equipment is relatively large and takes up costly space in the limited area of the casting room. Urethane systems are also known which are formed from urethane prepolymers and which are water cured. These have limited water resistance, poor molding properties and cure too slowly. Consequently, such systems are not satisfactory substitutes for plaster of paris for the rapid immobilization of fractures and are not used as primary cast systems, but rather, as secondary casts after healing has started. Also, the systems, in practice, are used with relatively large amounts of excess water, which creates the same problems as encountered with plaster of paris.
Systems using two different resin components in micro-encapsulated form are also known. But these are expensive to manufacture and require special mechanical or radiation equipment.
Other synthetic resin systems proposed involve the use of thermoplastic polymers. Tapes impregnated with the thermoplastic material are immersed in a tank of water at a sufficiently high temperature to soften the material and allow the tape to be applied. This is disadvantageous since a tank of temperature controlled water is required. Also, because of the presence of the water, the underwrap becomes wet and results in the same problems as with plaster of paris. Such thermoplastic resins exhibit limited heat resistance, poor molding characteristics and harden too slowly for rapid immobilization of fractures. As a result, the use of such materials has been primarily limited to use as cast replacements after healing is well advanced. These are relatively heavy, bulky and of coarse construction. Additionally, these plastic systems which are based on caprolactone are prepared for application by heating in a water bath at a temperature which substantially exceeds tolerable levels without the protection of insulated gloves.